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I BIME-002 I

B.Tech. — VIEP — MECHANICAL ENGINEERING (BTMEVI) Term-End Examination June, 2016 1-1091--4R BIME-002 : THERMAL ENGINEERING — I

Time : 3 hours

Maximum Marks : 70

Note : Attempt any seven questions. Use of Steam tables is permitted. Use of calculator is allowed.

1.

(a)

What are primary fuels ? List some important primary fuels.

(b) What is the difference between higher heating value (HHV) and lower heating value (LHV) of the fuel ? 5+5

2.

(a)

What is a fusible plug ? State where it is located in a boiler.

(b) Define 'Steam nozzle'. Explain with the help of neat diagrams, the various types of nozzles. 5+5

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P.T.O.

3.

In a boiler test, 1250 kg of coal is consumed in 24 hours. The mass of water evaporated is 13000 kg and the mean effective pressure is 7 bar. The feed water temperature was 40°C, heating value of coal is 30000 kJ/kg. The enthalpy of 1 kg of steam at 7 bar is 2570.70 kJ. Determine :

4.

5.

(a)

Equivalent evaporation per kg of coal

(b)

Efficiency of the boiler

10

A spark ignition engine has a fuel-air ratio of 0-067. How much kg of air per hour is required for a brake power output of 73.6 kW at an overall thermal efficiency of 20% ? Calorific value of the fuel is 42000 kJ/kg.

10

At a particular stage of a reaction turbine, the mean blade speed is 60 m/s and the steam is at a pressure of 350 kN/m2 with a temperature of 175°C. Fixed and moving blades of this stage have inlet angles of 30° and exit angles of 20°. Determine the blade height, if the blade height is one-tenth of the mean blade ring diameter and steam flow is 13.5 kg/sec at 350 kN/m 2 and 175°C. The specific volume of steam is 0.589 m3/kg.

10

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6. Air is expanded reversibly and adiabatically in a nozzle from 13 bar and 150°C to a pressure of 6 bar. The inlet velocity of the nozzle is very small and the process occurs under steady state flow conditions. Calculate the exit velocity of the 10 nozzle. 7. A turbojet engine flying at a speed of 960 km/h consumes air at the rate of 54-5 kg/s. Calculate (a)

Exit velocity of the jet when the enthalpy change for the nozzle is 200 kJ/kg and velocity coefficient is 0.97,

(b)

Fuel flow rate in kg/s when the air-fuel ratio is 75 : 1,

(c)

Thrust specific fuel consumption,

(d)

Thermal efficiency of the plant when the consumption efficiency is 93% and calorific value of the fuel is 45000 la/kg,

(e)

Propulsive power,

(f)

Propulsive efficiency, and

(g)

Overall efficiency.

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8. An engine uses a fuel of CV of 42000 kJ/kg and has a specific gravity of 0.75. The engine develops a brake power of 29.44 kW. The brake thermal efficiency of the engine is 24%. Determine the volume of the fuel consumed per second.

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9. A gas turbine is supplied with a gas at 5 bar and 1000 K and expands it adiabatically to 1 bar. Determine the exhaust gas temperature. Take C = 1.0424 kJ/kg K, Cv = 0.7662 kJ/kg K.

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10. Air enters the compressor of a gas turbine plant operating on Brayton cycle at 1 bar, 27°C. The pressure ratio of the cycle is 6. If WT = 2.5 We, where WT and We are the turbine and compressor work respectively, calculate the maximum temperature of the plant. Also determine the cycle efficiency. Take C = 1 kJ/kg K.

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